The present invention relates generally to the monitoring of industrial processes and, more particularly, to a method and apparatus for monitoring and/or controlling a process for producing a multilayer product including a base substrate and at least one layer of material deposited, coated or otherwise applied to the base substrate as it passes through a number of processing stations corresponding at least to the number of layers. While the present invention is generally applicable to monitoring and/or controlling the production of multilayer products which are produced by conjoining or applying layers to a base substrate regardless of the method of production, it will be described with reference to a coating processes to which the invention has been successfully applied.
A common way to measure and control the weight or thickness of a material coated on a substrate in an industrial manufacturing process is to measure the process before and after a coating station which applies the coating or layer to the substrate. The measurement taken before the coating station is subtracted from the measurement taken after the coating station to obtain the coating weight. Typically, the coating and the substrate are different materials and the calibration for the measuring or gauging instruments employed will be different for the two materials. The calibration of the gauging instrument succeeding the coating station in fact is dependent on the actual ratio of the coating weight to the substrate weight such that a measurement "catch 22" occurs in that the coating weight to be measured is required to be known to calibrate the gauging instrument used to measure it. Calibration of the gauging instruments is further complicated when the composition of the substrate varies within or between runs. Such substrate variation is becoming more common due to the increasing use of recycled materials such as paper in substrates and industrial applications which require deposition of the same coating materials onto many different substrates.
Accordingly there is a need for measuring and/or controlling a process for producing a multilayer product including a base substrate and at least one layer of material conjoined, deposited, coated or otherwise applied to the base substrate which simplifies calibration of measuring or gauging instruments. Preferably, the improved method and apparatus would permit measurement and/or control of the weight or thickness of each of one or more layers independently of the base substrate to which the layers are conjoined or applied yet permit measurement of the base substrate and intermediate stages of the multilayer product including the substrate and one or more intermediate layers if desired.